Made famous by the book and movie Into the Wild, Chris McCandless was a 24-year-old who hitchhiked out into the Alaskan wilderness, lived off the land, and died of starvation under extremely mysterious circumstances. Now, it seems the mystery of his death may have been solved.

Jon Krakauer, who wrote Into the Wild after McCandless' death twenty years ago, has spent the past two decades trying to figure out how the strapping young man died of starvation just a few miles away from a freeway that would have taken him back to civilization. In his book, Krakauer wrote that his hunch was that McCandless was somehow poisoned by the seeds of Hedysarum alpinum, also known as the wild potato.

Before his death, McCandless wrote in his diary that he'd been "weakened" by eating these seeds. Krakauer believed McCandless had eaten the seeds, then gotten so sick that he could no longer feed himself or hike to the road and get help. But nobody had ever identified the wild potato seeds as toxic. Even when Krakauer sent the seeds to a chemist, the results came back showing none of the toxins Krakauer expected to find. So Krakauer's hunch remained just a hunch — and rumors persisted that McCandless had starved out of sheer stupidity. He was just a college kid trying to rough it, and died when he couldn't find enough food.

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But the rumors didn't match the facts — McCandless had assiduously studied books on local wildlife, and was perfectly capable of hunting and gathering. Krakauer had almost given up on his poison theory when he saw a paper written by amateur scientist Ronald Hamilton, who connected Krakauer's strange situation with something he'd read about Nazi experiments in a concentration camp.

In 1942, as a macabre experiment, an officer at Vapniarca started feeding the Jewish inmates bread made from seeds of the grass pea, Lathyrus sativus, a common legume that has been known since the time of Hippocrates to be toxic. “Very quickly,” Hamilton writes in “The Silent Fire,”

a Jewish doctor and inmate at the camp, Dr. Arthur Kessler, understood what this implied, particularly when within months, hundreds of the young male inmates of the camp began limping, and had begun to use sticks as crutches to propel themselves about. In some cases inmates had been rapidly reduced to crawling on their backsides to make their ways through the compound …. Once the inmates had ingested enough of the culprit plant, it was as if a silent fire had been lit within their bodies. There was no turning back from this fire—once kindled, it would burn until the person who had eaten the grasspea would ultimately be crippled …. The more they’d eaten, the worse the consequences—but in any case, once the effects had begun, there was simply no way to reverse them …. The disease is called, simply, neurolathyrism, or more commonly, “lathyrism.”…

Hamilton suspected that the wild potato seeds had caused lathyrism in McCandless, paralyzing him before he could get help, and leaving him unable to get food.

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When Krakauer had those potato seeds tested twenty years ago, nobody had looked for the toxin in grass pea seeds — a neurotoxin called beta-N-oxalyl-L-alpha-beta diaminoproprionic acid, or ODAP for short. ODAP overstimulates nerve receptors, causing them to die — and the people most vulnerable to this toxin are men between 15-25, who are extremely physically active but aren't eating enough calories.

Sure enough, when those wild potato seeds were tested for ODAP, the results came back positive. Writes Krakauer:

To establish once and for all whether Hedysarum alpinum is toxic, last month I sent a hundred and fifty grams of freshly collected wild-potato seeds to Avomeen Analytical Services, in Ann Arbor, Michigan, for H.P.L.C. analysis. Dr. Craig Larner, the chemist who conducted the test, determined that the seeds contained .394 per cent beta-ODAP by weight, a concentration well within the levels known to cause lathyrism in humans.

According to Dr. Fernand Lambein, a Belgian scientist who coördinates the Cassava Cyanide Diseases and Neurolathyrism Network, occasional consumption of foodstuffs containing ODAP “as one component of an otherwise balanced diet, bears not any risk of toxicity.” Lambein and other experts warn, however, that individuals suffering from malnutrition, stress, and acute hunger are especially sensitive to ODAP, and are thus highly susceptible to the incapacitating effects of lathyrism after ingesting the neurotoxin.

Considering that potentially crippling levels of ODAP are found in wild-potato seeds, and given the symptoms McCandless described and attributed to the wild-potato seeds he ate, there is ample reason to believe that McCandless contracted lathyrism from eating those seeds. As Ronald Hamilton observed, McCandless exactly matched the profile of those most susceptible to ODAP poisoning.

Not only do we have strong evidence that McCandless died of toxin-induced paralysis, we also have some valuable information about what not to eat when you are hiking: wild potato seeds.